ctypes and cffi?

[paugier]

It is just a small and fast question. I see in the documentation: "Interface with the GMT C API directly using ctypes (no system calls)."

I understood that now, cffi was just better than ctypes for new projects (see for example https://www.quora.com/How-can-I-decide-between-using-ctypes-and-CFFI-in-Python).

I was wondering if there is a reason why gmt-python doesn't use cffi instead of ctypes?

[leouieda]

Hi @paugier, thanks for the link! I hadn't seen that post.

Basically, I didn't really know about CFFI until recently. I've been having a good experience with ctypes and numpy arrays have builtin support for it. Right now, I don't know if it's worth the trouble of switching if ctypes is working. But I'm open to suggestions if there is anything specific that CFFI can address.

Thanks for taking the time to give feedback! I really appreciate it.

[seisman]

Can we close this 2.5-year-old issue? I don't think we will switch to cffi in the next few years.

[weiji14]

Yep, close it as wontfix. But feel free to reopen if someone wants to work on it 🙂

[seisman]

Just tried cffi. The following example shows how to call the API function GMT_Get_Enum:

>>> from cffi import FFI
>>> ffi = FFI()
>>> ffi.cdef("int GMT_Get_Enum (void *V_API, char *key);")
>>> lib = ffi.dlopen("libgmt.dylib")
>>> lib.GMT_Get_Enum(ffi.NULL, b"GMT_VF_LEN")
32

For comparison, the ctypes version is

pygmt/pygmt/clib/session.py

Lines 263 to 280 in 5014591

	c_get_enum = self.get_libgmt_func(
	"GMT_Get_Enum", argtypes=[ctp.c_void_p, ctp.c_char_p], restype=ctp.c_int
	)
	# The C lib introduced the void API pointer to GMT_Get_Enum so that
	# it's consistent with other functions. It doesn't use the pointer so
	# we can pass in None (NULL pointer). We can't give it the actual
	# pointer because we need to call GMT_Get_Enum when creating a new API
	# session pointer (chicken-and-egg type of thing).
	session = None
	value = c_get_enum(session, name.encode())
	if value is None or value == -99999:
	raise GMTCLibError(f"Constant '{name}' doesn't exist in libgmt.")
	return value